SE-8802885-7 describes as previously known a gearbox of this type having two concentrically journaled input shafts, arranged to be driven alternately, and two lay shafts driven by said input shafts and having gears in engagement with gears on an output shaft. The inner input shaft is mounted in a roller bearing which is held in a bearing seat in a wall of the gearbox housing, and is provided with an axial bore into which there extends a shaft end of the output shaft. The proximal end of the shaft end is mounted in a roller bearing mounted in the bore and lies in the same radial plane as the proximal bearing of the input shaft, i.e. in the intermediate wall. The outer input shaft is mounted on the inner input shaft via an intermediate bearing which is disposed on the input side of the gearbox relative to the housing wall. The output shaft is in this manner journaled in the gearbox housing at both ends at the same time as the inner input shaft can be dimensioned with very little inner overhang, which eliminates the risk of excessive deflection of the two shafts.
The disadvantage of the arrangement described is, however, that the housing wall requires a certain amount of axial space making the gearbox longer and heavier than if the housing wall could be eliminated. A further disadvantage is that the lay shaft packages cannot be completely pre-assembled prior to installation in the gearbox housing, since they carry components which are to lie on either side of the housing wall. In this known gearbox, a central synchronization device on one lay shaft lies on the outside of the housing wall, while the rest of the components lie on the inside of the housing wall. On the second lay shaft outside the housing wall, there is a gear engaging a gear of the outer input shaft while the rest of the components lie inside the housing wall.